In a typical powder coating spray process, not all of the coating material that is sprayed adheres to the target substrate. The amount of powder coating material that actually ends up applied to the target substrate is a function of the transfer efficiency of the coating material. The average transfer efficiency for a coating material can be calculated by dividing the change in weight of the target substrate by the change in weight of the powder coating source dispensing the powder coating material. The transfer efficiency is conveniently expressed as a percentage of the powder coating material that adheres to the target substrate relative to the powder coating material that is sprayed.
The current practice is to measure the average transfer efficiency of a powder coating material by measuring the starting and ending weight of the target substrate and the total amount of powder sprayed. This is a time consuming, manually-intensive procedure. Moreover, this procedure does not measure the true transfer efficiency of a powder coating material due to the fact that the transfer efficiency values observed tend to vary over the course of the test cycle. In this regard, the transfer efficiency values observed with an uncoated or clean substrate at the beginning of the test are typically higher than at the end of the test when the substrate is coated. This is at least in part due to electrical insulating affects that result from accumulated powder on the target substrate. Until now it has not been possible to measure instantaneous transfer efficiency values at anytime during the test cycle, and this has prevented researchers from measuring the true transfer efficiency values of powder coating materials.
The present invention overcomes these problems by providing a method for measuring instantaneous transfer efficiency values of coating materials at any time during a test cycle. This permits measurement of the true transfer efficiency values of such coating materials. The term "true transfer efficiency value" is the transfer efficiency value of a coating material that is measured after start up of the test when the substrate is no longer "uncoated or clean" and prior to the point at the end of the test when electrical insulating affects caused by accumulated powder on the substrate lead to a deterioration or reduction in the observed transfer efficiency value.